THE INDIVIDUAL GROUPS OF PROTEINS 483 



Conversion into Hauwchromogen. 



The solution is made faintly alkaline with dilute caustic soda and 

 filtered. Stokes' reagent or ammonium sulphide is added to the 

 filtrate. The two characteristic bands of haemochromogen are seen 

 with a spectroscope in the green region. 



Acid HcEHiatin in Alcohol. 



Acid haematin is soluble in alcohol. A solution is most readily obtained by 

 adding sufficient alcohol to blood to precipitate the proteins. The precipitate 

 is warmed with alcohol containing i per cent, of sulphuric acid. A dark-brown 

 solution of acid haematin showing the absorption bands is obtained. 



Acid Hcematin in Ether. 



Acid haematin dissolves in ether. An ethereal solution is prepared by 

 adding half the volume of glacial acetic acid to defibrinated blood and an 

 equal volume of ether and mixing thoroughly. The ethereal solution of acid 

 haematin rises to the surface. On pouring it off into a clean vessel and 

 examining it with a spectroscope it will show the characteristic band in the 

 red region and a broader band between D and F. This band is resolved 

 into two bands if the solution be diluted with acid ether (i part of glacial 

 acetic acid to 2 parts of ether). There is a narrow band in the light green 

 to the red side of E and a broader, darker one in the green. A fourth very 

 faint band may be seen on the violet side of D. 



Alkaline Hcematin. 



Dilute defibrinated blood (i : 5) is mixed with half its volume of 

 alcoholic caustic soda solution and heated gradually nearly to the 

 boiling-point The colour becomes brown. On cooling and shaking 

 with air (reducing substances are formed by the action of alkali and 

 may reduce the haematin to haemochromogen) and examining the 

 solution with a spectroscope, a broad but very faint band will be seen 

 to the red side of D, extending a short distance towards the violet 

 side. The blue end of the spectrum is considerably absorbed. 



Alkaline H&matin in Alcohol. 



Alkaline haematin is soluble in alcohol and is prepared by mixing a little 

 defibrinated blood with solid potassium carbonate so as to form a paste and 

 evaporating to dryness on the water-bath. The dry residue is boiled in a 

 flask on a water-bath with alcohol. The filtered solution shows the absorption 

 band of alkaline haematin. It is more distinct than with the aqueous solution. 



Conversion into Haemochromogen. 



A few drops of ammonium sulphide are added to the alkaline 

 solution and warmed. The solution becomes red in colour and on 

 spectroscopic examination shows two bands in the green, the one 

 nearer D being very prominent and sharply defined, the other being 

 much fainter. 



In very dilute solutions only the one band is seen but the absorp- 

 tion of light here is very great. A solution of oxyhaemoglobin, where 

 the absorption bands can scarcely be seen, on conversion into haemo- 

 chromogen, will show this single band. 



The conversion of haemoglobin into haemochromogen is a very 

 delicate test for blood stains; the stain is heated with I per cent, 

 caustic soda, the solution is cooled and filtered and then reduced. 

 Examination with the spectroscope shows one or both absorption bands. 



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